Known inflatable craft suitable for white-water use can be generally categorised as canoes/kayaks, catamarans, or rafts, although there is a degree of overlap with some hybrid craft.
Typical inflatable canoes or kayaks are approximately symmetrical about their lateral and longitudinal axes, with enclosed sterns, and utilise oars or paddles for propulsion. Although the use of hands is a possible alternative, it is impractical to use feet/leg power for manoeuvring and propulsion. Entry to, or exit from the canoe to the water is hindered by the inflatable tube forming the whole perimeter.
An intrinsic feature of canoe design is that they are very long in relation to their width, and thus somewhat constrained in their ability to manoeuvre in confined areas.
Catamarans with inflatable hulls, such as disclosed in U.S. Pat. No. 5,290,196, whilst enabling unobstructed access into and out of the seating position, require a rigid tubular frame to form the seat and secure the hulls. Although the seat can be folded flat to facilitate overland transport, via attached shoulder straps, the float is primarily intended for flat-water use, in particular for fishing/hunting: the seating position is high, relative to the hulls, and would be precarious for white-water use, given the relatively short hulls.
Inflatable catamarans capable of white-water use are required to be substantially bigger to achieve the required stability as the operator is sifting at a significant height above the water surface.
In order to obtain sufficient stability to minimise the risk of capsize together with the associated structural requirements, such craft tend to be substantial, expensive, cumbersome and unwieldy. In contrast to the kayaks/canoes, foot propulsion on catamarans is possible, but the width of the inflatable hulls and the height of the occupant above the water inhibit practical use of the hands and thus oars are generally utilised.
White-water rafts formed from a continuous inflatable tube in an elongated annular shape, with a rigid, semi-rigid or flexible floor, are well-known. They generally require several users, equally distributed on each side of the raft using paddles to propel and steer effectively. Again, foot propulsion is impractical.
Several types of floats suitable for non-white-water use are known, such as ring floats, tubes, horseshoe floats, chairs and pool floats/toys.
Annular inflatable tubes used by fisherman to access areas of a lake or stream unreachable from the shore are typically formed from a car tyre inner tube (or similar) covered by a fabric sleeve. A fabric seat is suspended from the ring allowing the whole of the lower torso to be submerged in the water and supporting the user in an upright position. Waders and swim fins are used by the fisherman in conjunction with this type of float. A drawback of such designs is the difficulty in getting in and out of the tube (especially when suitably attired for fishing) both ashore and following a puncture in the air bladder whilst in water.
The seating position is hydrodynamically inefficient and exposes the user's lower torso to underwater hazards, thus making white-water use in shallow rivers impractical.
Variations on annular inflatable designs are disclosed in U.S. Pat. No. 4,601,667, and NZ patent No. 61408. These all teach a seating position which may be maintained above the water, allowing just the lower legs to be submerged. Neither of these floatation devices has an efficient hydrodynamic shape or is suitable for white-water use due to the risk of injury from underwater obstructions. Ease of entry and exit from the water is again problematic.
U.S. Pat. No. 5,474,481, (continuation-in-part from U.S. Pat. No. 5,297,978) discloses a "diving well" inside the perimeter of the inflatable tube, with an elevated seating position with just the lower legs capable of immersion. The hull shape is however, restricted to an ovoid/annular shape. This configuration prevents the efficient, unrestricted use of flippers and due to the relatively large width of the float, hand propulsion is impractical, necessitating the use of oars and/or a motor.
To obviate some of the problems posed by such annular shaped floats, a number of horseshoe or "U" shaped--floats have been developed.
U.S. Pat. No. 5,217,400 discloses a U-shaped float formed by a single continuous tube with a flexible seating platform attached between the legs of the U. A tensioning strap attached to the end of the legs extends around the outside perimeter of the float. This strap is required to prevent the opposing legs collapsing towards each other under the weight of the user in the seat. Furthermore, the underwater profile of the hull makes no concession to hydrodynamic efficiency. The seating position is upright, being configured primarily to permit the user to engage in stationary activities such as fishing or hunting, rather than being optimised as a means of transport on the water. No protection would be available to the user's lower body in shallow and/or white-water, from any sub-surface hazards and the float has insufficient length relative to its width to provide stability in turbulent water.
The above mentioned requirement to maintain the structural integrity of an open-ended float has been addressed by differing means as disclosed in the following patents and designs:
U.S. design No. 341866 employs a "V" shape using a single tube of generally circular cross-section, with substantially more volume (and therefore buoyancy) in the apex of the V. The seat appears to be composed of a simple mesh fabric. The angular divergence of the two "hulls" gives some structural resistance to the weight of the user in the seat. Again, there is no consideration of the hydrodynamic efficiency of the hull form, nor to the protection of the user from submerged obstructions/hazards. In particular, the blunt shape of the region of the "V" together with the increased volume both contribute to reduce the directional stability and the potential speed of the float.
U.S. design No. 355466. This design incorporates a lateral bar spanning the open end of a U-shaped float.
U.S. design No. 349744. Similar to U.S. design No. 355466 but without the rear cross-member and with the inclusion of an additional seating well in the bow.
Both U.S. design No. 355466 and U.S. design No. 349744 have generally circular cross-sectional float tubes and a flat seat, parallel with the water surface, and appear to be designed for use as a recreational toy in swimming pools or similar non-dynamic environments. The proportions of both design would provide virtually no upper body support for a user positioned to be able to immerse their legs from below the knee for paddling.
U.S. design No. 362706. This shows a rectangular fishing float with a centrally-mounted rigid seat and a rectangular cut-out to enable the fisherman's lower legs to dangle in the water. The whole shape of this design is clearly not intended to minimise the friction of the hull through the water.
None of the above referenced patents/designs display any rocker at any of the sides/ends of the floats, with the profile of the underside being substantially parallel to the water's surface.
U.S. Pat. No. 1,465,790. This is a non-inflatable U-shaped float in which the users legs and lower torso are submerged during use. A seat suspended from the centre of the "U" holds the user in an upright position.
U.S. Pat. No. 1,503,624. This discloses a rigid, non-inflatable U-shaped float, with which the user adopts a prone position with their arms extending outside and to the front of the float. This permits a swimming action to be carried out with both the arms and legs. The whole of the user's lower torso is submerged in the water.
There are also various miscellaneous floats, which do not fall into the previously described categories, which are broadly relevant.
U.S. Pat. No. 3,543,712 teaches a swimming aid which is contoured on its upper surface to match the upper torso of the user, thus leaving the arms and the body below the hips free to move. The user adopts a prone position and can utilise means of powered proportion incorporated in the float, in addition to the arm and leg swimming action.
While some lateral stability is provided by the longitudinal "keel-like" underwater projections, the float would afford little protection to the user in a white-water environment.
U.S. Pat. No. 5,186,667. This floating hammock places the user in a face-up, reclining seating position. However, it is clearly not intended to facilitate any means of user propulsion and indeed, incorporates supports/rests for both the arms and feet. The user's midriff is immersed in water entering a via lateral openings in the side of the hammock. The float does not have an open transom, contains little structural integrity and is not robust enough for white-water use.
U.S. Pat. No. 5,360,360. This inflatable device is specifically intended for towing, both on the water and over snow. While the general appearance of the hull is U-shaped, the user or users is/are intended to sit/kneel/stand behind the side-walls. These walls are designed to provide protection from the effects of the elements whilst being towed. The underside of the float is flat and is intended to skim the surface of the water/snow rather than for human propulsion. While leg propulsion would be possible when not under tow, paddling by hand would be hindered due to the relatively high sides of the float.